The invention relates to a device and a method for monitoring electromechanical brake application devices for vehicle brakes.
Spring-type accumulators are used mainly for operating parking brakes in the commercial vehicle field, in which the required manual force for operating a cable brake can no longer be applied by the driver. In the case of lighter vehicles, a parking brake effect is achieved mainly by a pure cable mechanism. The driver operates a lever at whose one end a Bowden cable is fastened which exercises a braking force upon normally two wheels of the vehicle.
Generally spring-loaded cylinders are designed such that a tensile or pressure effect occurs when the cylinder is ventilated. The operating force for the wheel brake is applied by a strong pressure spring which is supported on the housing of the cylinder and transmits the tensile force by way of a spring plate and a ball support to the piston rod. In its drive position, the cylinder is ventilated by way of a hand brake valve. For the braking, the pressure in the ventilated space is lowered by way of the hand brake valve. Corresponding to the lowering of the pressure, the pressure spring pulls the piston rod into the cylinder, whereby the wheel brake is operated. The spring chamber is ventilated by way of the expansion bellows.
Particularly in the case of rail vehicles, in addition to the pneumatic operation of the spring-loaded cylinder, the use of an electric-motor drive has also been discussed for tensioning the spring of the spring-loaded cylinder. A brake application device of this type is known, for example, from European Patent Document EP 0 129 969. This document shows a brake application device for rail vehicle brakes, in the case of which the drive shaft of an electric motor drives a threaded spindle of a threaded transmission. The rotatable threaded spindle is axially fixed and carries a recirculating ball nut which is disposed in a spring plate which continues into a push pull tube which is connected with a brake linkage for operating the brake shoes of a disk brake for rail vehicles. During the application of the brake, the push pull tube is pressed by an accumulator spring out of the housing to the outside. When the electric motor is acted upon by current, this electric motor tensions the accumulator spring by way of the threaded drive, which accumulator spring, during its contraction, withdraws the push pull tube into the housing and thus releases the brake.
The electric motor or rather the driven shaft of the electric motor is arranged essentially parallel to the threaded spindle of the threaded drive, a pinion being disposed on the output shaft of the electric motor, which pinion drives another pinion mounted on the threaded spindle.
A method of this type and a device of this type are known from German Patent Document DE 197 41 869 A1. This document illustrates a device for monitoring electromechanical brake application devices for vehicle brakes, in the case of which the brake application device, among other things, has a drive which comprises an electric motor with a current supply and a spring-type accumulator with a spring which can be tensioned by the drive for operating a tappet for the application and release of the vehicle brake. A diagnostic possibility is ensured by the electric operation of the electric motor.
The invention has the object of creating, by means of a simple device, a (particularly electronically operating) monitoring device as well as a monitoring method by which operating disturbances can be detected already in an early stage, so that a service or repair measure can be initiated before a detectable impairment of the operation of the brake application device or even a failure of the spring-type accumulator occurs. In particular, the monitoring device as well as the monitoring method should also be suitable for monitoring brake application devices with electromechanical spring-type accumulators.
The invention reaches this goal with respect to the device and with respect to the method according to the invention.
The monitoring device has a detection unit constructed as a sensor for detecting the current and/or voltage curve of the current supply, whose output is connected to an evaluating unit which is designed for comparing the detected current and/or voltage curve with previously stored desired values and/or previously stored desired value characteristics (and possibly emitting a fault signal on the basis of the comparison).
By means of the invention, the operating safety and reliability of the electromechanical spring-type accumulators can clearly be increased in comparison to spring-type accumulatorsxe2x80x94also with pneumatic release pistonsxe2x80x94which do not have such monitoring devicesxe2x80x94while the (additional) costs are low.
The invention is based on the recognition that the at least one drive (electric motor) used for releasing the electromechanical spring-type accumulator is also driven during the initial braking by the force of the springxe2x80x94preferably by way of a spindle drive and a wrap-type and/or geared transmission. In this condition, the electric motor acts as a generator so that it generates current and so that a voltage is applied to it whose amounts depend essentially on the achieved rotational driving speed and possibly on the connected electric consuming devices. In the event of the faultless functioning of the spring-type accumulator, during an initial braking, a characteristic current or a characteristic voltage is therefore generated at the motor. These characteristic values (or even functions) may be filed in a memory and may be called up by the evaluating unit (which may, for example, be partxe2x80x94particularly softwarexe2x80x94of an EBS control unit).
Almost any disturbance in the operation of the electromechanical transmission system causes a changed rotational motor speed and thus affects the emitted generator voltage (or generator current). This starts in the case of trivial damage, such as broken or cold soldering joints, defective line cables or plug-type connections. In addition, also disturbances, such as sluggishness or even scuffing of the circulating ball spindle, of the transmission gear, of the spring-type accumulator piston, or a slipping or completely locking magnetic brake can be determined. If an operational disturbance occurs in the electric motor itself, such as a melted winding, a worn-out or broken brush, this also has a direct effect on the emitted current or the applied voltage. The breakage of a force-transmitting or torque-transmitting component can also be immediately detected. The evaluating unit is therefore preferably designed for comparing the detected curve of the current and/or voltage with previously stored desired values and/or with a previously stored desired-value characteristic during a generator operation of the electric motor.
With respect to the method, the invention achieves its object in that, by means of the detecting device, the curve of the current and voltage in the current supply is monitored at least in the generator operation and/or in the motor operation of the electric motor and is compared by means of the evaluating unit with previously stored desired values or with a previously stored desired-value characteristic, in which case, when deviations occur from the previously stored desired values or the previously stored desired-value characteristic, a fault signal is generated.
In addition to the monitoring of the voltage or current at the electric motor, it is expedient to place additional sensors for supplementary purposes in the system. Preferably by means of distance sensors (for example, inductively) on the threaded spindle, the precise position of the spring-type accumulator and thus the amount of the braking force is determined. For the purpose of the monitoring, the spindle position is also determined during the drive. By means of a pure voltage or current monitoring, it is, for example, not possible to detect a very slow closing of the brake during the drive because in principle no current is generated by the electric motor, as expected also during a correct operation. In addition, this sensor is used for promoting and supplementing the monitoring of the voltage or current.
With its aid, it is even possible to use the spring-loaded brake as an emergency brake or service brake. As a result of the fact that the force at the brake is determined by the spindle position, the distance sensor is simultaneously used as a braking force sensor. Thus, a brake signal given by the driver corresponding to the braking desire can be converted to a defined braking force at the wheel.
Instead of a distance sensor, the use of a different type of displacement transducer is also possible; for example, a rotation transducer at the spindle nut or at the roller bearing or an angle sensor. As a result, by means of a corresponding conversion, a conclusion can be drawn with respect to the travel path of the spindle and thus with respect to the braking force.
According to another variant of the invention, the application device of the disk brake comprises a holding device which has a mechanically and/or electromagnetically releasable brake which generates the force for holding the spring (particularly mechanically). For example, a disk-type spring pressure brake, which is known per se, can be used for this purpose. In contrast to the prior art of the above-mentioned type, the force for holding the spring-type accumulator is applied mechanically. This results in the advantage of a minimal current consumption while the durability is prolonged.
Additional advantageous further developments of the invention are contained in the remaining subclaims.
In the following, the invention will be described in detail by means of embodiments with reference to the drawing.